Electric gaseous discharge device electrode



y 17, 1951 H. H. HOMER 2,560,953

ELECTRIC GASEOUS DISCHARGE DEVICE ELECTRODE F1106 June 30, 1949 5 II N u6 R II H/ F6 2 INVENTOR.

Horace f7omer LZZWM ATTORNEY Patented July 17,1951

UNITED STATES PATENT OFFICE.- ELECTRIC GAsgloEfigizggwGE DEVICE I Horace1!. Homer, Arlington, Mass., assignor to.

Sylvania Electric Products Inc., Salem, Mass a corporation ofMassachusetts 7 Application Lime so, 1949, Serial No. 102.304

2 Claims. (Cl. sis-17s) This invention relates to electric gaseousdischarge devices and more particularly to.fiuorescent lamps.

In the manufacture of electric gaseous discharge devices, and moreparticularly in the manufacture of fluorescent lamps of the hot cathode"type, i. e., those in which the electrode comprises a coiled filament oftungsten wire, such as that shown in U. S. Patent 2,258,158,."forexample, the electrodes are usually provided with a coating of anelectron-emissive material. In the case of a fluorescent lamp electrode,the electron-emissive material usually comprises an oxide of one or moreof the alkaline earth metals. For convenience, the alkaline earth metalsare usually appliedin the form of a carbonate hich breaks down to theoxide when the lamp is processed.

During the operating life of fluorescent lamps. an objectionablediscoloration frequently appears on the wall of the lamp near the endsthereof and in proximity to the electrodes. One form which thisdiscoloration may assume is a. light yellow, brownish or black ring orband which usually extends completely around the periphery of the innerwall of the lamp. This particular discoloration is usually defined by asharpedge on the side near the electrode and a diffused edge on the sidenear the longitudinal eenter of the lamp. These rings or hands areusually found forward of the electrodes withthej sharp edge locatedadjacent to an end of the positive column or plasma. 7 jAn object ofthis invention is to retard the development of this discoloration.

' Further objects, advantages and features will be apparent from thefollowing description when read in conjunction with the accompanyingdrawing in which:

Figure 1 is a side elevational view of a fluorescent lamp with an endthereof broken away. showing the electrode mount structure.

Figure 2 is an enlarged fragmentary detail of the electrode mountstructure shown in Figure 1.

In Figure l, the lamp I comprises an elongated tubular glass envelope 2,the inner wall of which is provided with a coating 3 of fluorescentmaterial, and electrode mounts 4 (one of which is shown) sealed in theends thereof. Each electrode mount comprises a glass stem 5 having aflared portion 6 which is sealed to the glass envelope 2, a press Ithrough which lead wires 8 are sealed, and a filamentary electrode 9 oftungsten wire mounted on the lead wires. At least one of-the stems 5 isprovided with an aperture 'ZrLsmps I. therein to which an exhaust tube(not shown) is connected to permit evacuation of the lamp envelopeduring processing. The sealed envelope is provided with a filling ofinert gas at low pressure, such as argon at about 3 mm. and a smallquantity of mercury II.

The filamentary electrode 91s a tungsten wire which has been coiled onceto define a' primary coil and then a portion thereof intermediate theends is coiled again to define a secondary coil. A quantity ofelectronemissive material .12, such as an oxide of one or more of thealkaline earth metals, is disposed primarily within the turns of thatportion of the primary, coil which has been provided with a secdndarycoiling. The electrode 9 is supported on lead wires 8 by clamping orwelding the lead wires 8 to the ends or legs II of the primary collthereof.

I have discovered that the development of discoloration on the wallofthe lamp envelope during life can be arrestedsubstantially-by providingthe legs I! of the filamentary electrode with a reservoir of powderedzirconium is preferably disposed within the turns thereof. Table I belowillustrates this quite clearly. This table reflects the results of atest in which'the legs of the filamentary electrodes of several lampswere provided with the powdered zirconium and the legs of thefilamentary electrodes of several other lamps were not so provided. Theformer are identified as Zr lamps"; the latter as controls.- Thediscoloration at the end of varioushours of burning is in terms ofarbitrary relative-unit's.

Table I Discoloration at- 100 Hours 600 Hours 875 Hours 2. 5 7. 6Controls 0 2i. 3 4,3. 3

I have found that the location of the powdered zirconium on thefilamentary electrode mount is quite critical. For example, whenpowdered zirconium is placed on the lead wires instead of on the legs ofthe filamentary electrode, the lamps are hard to start, their brightnessis diminishcd,

' and the color of the light emitted is affected.

The powdered zirconium is applied to the legs of the filamentaryelectrode in the form of a suspension thereof in a suitable medium. Forexample, it may be prepared by adding powdered zirconium to a solutionof borated silica in isopropyl alcohol.

The borated silica, hereinafter referred to as solution A, is preparedby adding an excess of anhydrous B203 to isopropyl alcohol, agitating ina closed vessel for about 24 hours, and filtering. The filtered solutionshould contain not less than .03 gram B20: per cc. of alcohol. This issolution A. o

A second solution, hereinafter referred to as solution B, is prepared byslowly heating 100 cc. of ethyl silicate with 40 cc., of .6N HCl andconstantly stirring the same until completion of the reaction.Completion of the reaction has beenv eflected when the initial two phasesolution becomes one phase; at the same time there is an evolution ofheat and fine bubbles. Solution A is then added in the ratio of threeparts of solution A to one part of this solution. This mixture is thenpermitted to stand for about 24 hours and is then decanted. The decantedsolution is solution B.

The solution of powdered zirconium, which is applied to the legs of theelectrode, is prepared by adding powdered zirconium to a mixture ofsolution A and solution B in the following pro portions: powderedzirconium 500 grams; solution A 110 cc. and solution B 40 cc. However 1othersuitable suspension media and binders may be employed withoutdeparting from the spirit of the invention.

In the preferred embodiment of my invention the suspension of powderedzirconium is uniformly distributed and completely fills the intersticesof the legs of the electrode. However, this condition is not necessaryfor the attainment of all the beneficial effects of my invention.

What I claim is:

1. An electric gaseous discharge device electrode comprising: a tungstenfilament having coiled legs, and a coiled coil portion intermediate thelegs; a quantity of electron-emissive material on said coiled coilportion; and a quantity of powdered zirconium within the interstices ofsaid coiled legs only of said filament.

2. An electric gaseous discharge device comprising: an elongated sealedglass envelope; a

filling of inert gas at low pressure in said envelope; a small quantityof mercury in said envelope; a tungsten filament in said envelope ateach end thereof, each filament having coiled legs and a coiled coilportion intermediate the legs; a quantity of electron-emissive materialon said coiled coil portion; and a quantity of powdered zirconium withinthe interstices of said coiled legs only of said filament.

HORACE H. HOMER.

REFERENCES CITED The following references are of record in the file ofthis patent: 1

UNITED STATES PATENTS 2,462,837 Braunsdorfi Mar. 1, 19.49

